The oligomerization of light olefins (typically mixtures comprising propylene and butenes) to heavier olefins is important for the production of gasoline, distillate, and feedstock for other processes (e.g., C6 to C14 olefins converted in the Oxo Process, hereinafter “Oxo”, to functionalized products such as aldehydes and alcohols). See, for instance, U.S. Pat. No. 3,657,150. Typical commercial processes employ multiple reactors filled with solid phosphoric acid catalyst (SPA catalyst).
For the production of distillate and feeds to Oxo, there is a need for trimer selective catalysts, e.g., conversion of propylene selectively to nonenes as Oxo feedstock, and conversion of butenes selectively to dodecenes for use as high quality, low sulfur diesel or jet fuel. Efforts to increase the yield of linear or near linear trimers using, for instance, zeolite catalysts, have not significantly solved the problem. See, for instance, WO 95/22516.
U.S. Pat. No. 4,587,368 uses the delayed addition of fresh monomer to improve the yield of tetramers and pentamers of alpha olefin monomers. Prior to delayed addition of monomer, the trimer yield is “in excess of 20% or even 25%, by total oligomer weight”. After staged addition of monomer, the yield of trimer decreases.
A process for oligomerization of lower olefins in paraffin-containing mixed aliphatic feedstock to yield branched intermediate olefins is disclosed in U.S. Pat. No. 5,134,242. Selectivity of conversion of propylene to nonene as high as 62% is reported.
U.S. Pat. No. 5,811,608 teach the production of saturated oligomers wherein the saturation of the heavy olefins is improved by the recycle of the heavy paraffins to the oligomerization zone. The recycle is said to inhibit fouling of the oligomerization zone and improves selectivity to C8 isomers. See also U.S. Pat. No. 5,895,830.
U.S. Pat. No. 6,072,093 utilizes a recycle of cycloparaffins in a process for oligomerizing light olefins to heavier olefins. The recycle is said to extend the catalyst life.
U.S. Pat. No. 6,143,942 utilizes a two-catalyst system said to maximize the proportion of nonene resulting from the oligomerization of propene. The patent suggests that C3 monomers are converted to hexenes by one of the catalysts (ZSM-22) and the other catalyst (ZSM-5) converts hexenes to nonenes by reaction with propene. A selectivity as high as about 51% is observed.
The yield of nonene using a feed of predominantly propylene is said to be maximized by “optimizing the reaction conditions”, according to U.S. Pat. No. 6,403,853. Selectivity of as high as 48% to nonene is exemplified.
Other references of interest include U.S. Pat. Nos. 5,672,800; 6,649,802; and 6,911,505.
The present inventors have surprisingly discovered that olefin monomers can be selectively oligomerized using zeolite catalysts by providing feedstock under suitable conditions to optimize the yield of trimers of said monomer.